function getLabel(id) {
    return document.getElementById(id);
}
function changeSec() {
    //得到myspan值，每秒减一，会进行隐士转换
    getLabel('myspan').innerText=getLabel('myspan').innerText-1;
}
var mytime = setInterval("changeSec()",1000);
//五秒后跳转
function tiao() {
    clearInterval(mytime);
    //window.open("./welcome.html","_self");
    window.location.href = "./index.html";
}

setTimeout("tiao()",5000);